Electra Sportster (oz13604)

About this Plan

Electra Sportster. Electric sport model. Wingspan 52 in, wing area 496 sq in. For electric power with Astro 05 motor with 2.5:1 belt drive.

Quote: "Electra Sportster, by Hal deBolt. A revolutionary electric that sparkles.

IF YOU'VE been studying electric-powered designs as I have, you will have noted the similarity of them. They seem more free flight in nature than they do R/C, especially in structure and their generous size for the power used. With recent advancements in the power department, the Electra Sportster is an example of what can be done in the other direction. This is an R/C type model powered by electric with the appearance and performance of a typical Sunday flyer sport engine-powered plane. The construction is also typical R/C with some new twists.

The success of this design comes from trading off excess structure weight to compensate for the necessary dead weight. The low power loading is made up for by using a very efficient wing, and letting the wing do most of the work instead of depending on the motor. Also when the power loading is low, drag reduction becomes an even more important asset. Reducing drag by some fraction can be equal to adding a similar amount of power.

There is very little unusual here in the aerodynamics department. What you see is another good looking R/ C sport design with some careful attention to detail. The wing is of the most importance and uses a low drag, laminar flow, symmetrical section with good lift characteristics. We do want aerobatic capability. The force arrangement is 'modern pattern' in nature, again assuring minimum drag. The result is neutral stability with aerobatic capability.

Construction: You'll note that this is not a 'glue A to B' type construction article. Instead I'll detail features that can help anyone build lightly using Ri C style structure, suitable to electric power.

The light weight is accomplished by depending completely on 'stressed skin' for strength. Note that the stabilizer is nothing but light sheeting over 1/16 ribs. While the leading and trailing edges are 1/4 inch wide, very little is left after shaping. The completed tail components only weighed 1 ounce.

Adding to the stressed-skin wing strength is the Micafilm covering, which is very light and has great tensile strength.

The nearly 500-square-inch wing includes the landing gear mount and ailerons at a bare weight of 4-1/2 ounces. Ready to fly, it was just 6 ounces.

Throughout the structure note many weight-reducing features; each minor perhaps, but important to the total. For example, the ailerons do not have torque rods, just elevator style horns. The elevator joiner is balsa, not metal or hardwood. The tail skid is a bit of plywood, and no tail wheel is needed. All hinges are polypropylene plastic strips with practically no weight. You slip them into a slit made with an X-Acto knife and add a drop of Jet. The result is simple and tight.

The fuselage uses a birch ply motor mount bulkhead with many holes and no blind nuts, which is quite light and strong. The 3/32 sheet sides only have wing saddle doublers and 1/2-square-inch corner longerons, just about minimum. Note that the servo rails go through the fuselage sides, eliminating a bulkhead and reinforcing in that area. The two main bulkheads are Lite-ply for needed wing attachment strength but light as a result of the holes used. I used 1/16 wire pushrods on the prototype, which checked out lighter than other types.

While the finished cowl looks very professional, producing it is quick and easy. After the fuselage is covered, attach the belt drive. Next fit a 1/8 former tightly around the unit base. Shape the outside of the former to the fuselage contour and then undercut slightly to allow for the fiberglass thickness. Leave it in place. Match a 1/16 ply ring to the spinner backplate. Size the ring's inner hole to be a press-fit on the propeller drive washer. Align the ring on the drive washer 1/16 inch back from the front face to allow spinner clearance.

With the ring and former in place, fit pieces of foam between them around the belt drive. Just tack-glue them in place..."

Electra Sportster, MAN, May 1985.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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